When a gas pipe breaks, several types of repairs may be desirable. If there is pressure in the pipe on both sides of the break, all that is necessary is to seal the pipe on both sides of the break. This allows service to be continued while the isolated section of pipe is repaired. Alternatively, gas may be fed through the pipe, under pressure, from a single source to consumers. In that event, if a break occurs between the source and the point of demand, and the pipe is sealed upstream of the break, all points downstream of the seal will be cut off from gas until the repair is made. If service is to be continued to consumers both upstream and downstream of the seal while the repair is being made, it is necessary to install a bypass around the break.
Gas pipes may be either metal or plastic, usually polyethylene. When a polyethylene gas pipe breaks, and the pipe is sealed so that it may be repaired, the seal is made by pinching. The apparatus necessary to effect this operation is quite large, since typical gas pipelines are about two inches in diameter and have a wall thickness of 3/16". Moreover, pinching the pipe in this manner and then reopening it by returning it by force to its initial round shape, weakens the pipe, making it vulnerable to breaks which may not occur until months later. This is particularly so in cold climates.
Machines exist whereby pipe may be sealed by boring a hole in the pipe on either side of the break, inserting a bypass stopper or plug through each of the holes, establishing a bypass connection between the two bypass plugs, repairing the break, and permanently sealing the inlets to the pipe where the bypass connection was made. Such machines include a fixture that permits a succession of tools to be applied to the pipe through a branching saddle while there is pressure in the pipe, the fixture including valving to permit the tools to be inserted and removed, notwithstanding the escape of gas under pressure from the pipe into the fixture. Existing fixtures of this type fail to maintain proper alignment between the pipe and the tools that are inserted into the pipe through the fixture. As a result, the tools tend to enter the pipe at an angle other than 90.degree. to the pipe's centerline, an undesirable condition. Moreover, such fixtures tend to bend the pipe while it is being worked on, because the fixtures are affixed to the pipe by means of a pair of brackets which straddle that portion of the fixture through which tools are inserted into the pipe. Consequently, as pressure is applied to the tools and through them to the pipe, the pipe bends, due to the bending moment between the tools and the brackets on either side of them.
In the parent application Ser. No. 07/513,599, of which this is a divisional application, there are described and claimed an apparatus and a method for sealing a gas pipe carrying gas under pressure, without deforming or bending the pipe and, if desirable, for providing a tap in that gas pipe whereby a bypass around a damaged section pipe may be effected. The apparatus and method of the are particularly adapted for use with a branching saddle, which is bonded by conventional means to the side of the pipe, plugging or tapping of the pipe being accomplished through the cylindrical pipe stub of the branching saddle. In carrying out the method, a series of operations necessary to accomplish the above objectives are performed by providing a set of tools, each for one of the operations. Each tool has a sealing plug, a shaft slidably extending through the plug, and a tool at the end of the shaft, movable between extended and retracted positions by sliding the shaft in the plug, the tool having a retracted position when it is nearest the plug and an extended position when it is farthest therefrom.
To allow the tools to perform their respective operations, there is provided a fixture having a wall defining a pressure chamber, divided by a valve into upper and lower portions. An upper inlet leads into the upper chamber portion, and a lower inlet leads into the lower chamber portion, there being additionally provided a valved pressure-release port leading through the side of the wall into the upper chamber portion.
In preparation for performance of the series of operations, a branching saddle having a cylindrical pipe stub is bonded to the pipe, the pipe stub extending at an acute angle to the pipe. The fixture is mounted on the pipe so that the stub enters the lower inlet of the fixture. Thereafter, successive ones of the tools are sequentially and individually inserted in the upper inlet so as to seal it, and, while so inserted, each tool is manipulated in conjunction with the valve and the valved pressure-release port so that the upper chamber portion is not pressurized while the tools are inserted or removed. In particular, each tool is inserted into the upper inlet while the tool is in its retracted position, until its sealing plug is fully seated in the upper inlet of the fixture. Thereafter, the valve which divides the fixture's upper and lower portions is opened and the tool is advanced into its extended position, wherein it engages the pipe through the branching saddle. Upon completion of the tool's operation, it is withdrawn to its retracted position, above the valve, which is then closed, and the valved pressure-release port is opened, after which the tool is removed from the fixture.
To allow the above method to be performed, there is disclosed apparatus which comprises at least one insertion assembly, including a shaft, a tool attached to the end of the shaft, and a cylindrical, externally-threaded sealing plug mounted slidably on the shaft. The insertion assembly is received by a fixture comprising a barrel having an internally-threaded inlet at one end for receiving the sealing plug, a second inlet at its opposite end for receiving a fitting, such as the branching-saddle pipe stub, and a bore extending between those ends. Between opposite ends of the barrel is a first valve for separating the bore into first and second mutually-pressure-isolated regions. A valved opening is provided for releasing pressure from the bore region nearest the threaded inlet, through the side of the barrel, prior to removal of each insertion assembly. A second, valved opening may be provided to allow gas to be diverted past a section of the pipe through the other bore region.
The fixture is installed by the expedient of means for attaching the barrel to the pipe so that the fitting on the pipe enters the second inlet of the barrel. Significantly, the tool carried by the insertion assembly is retractable into the bore region between the first, threaded inlet and the first valve and is extendable into engagement through the fitting with the pipe when the first valve is open.
Typically, the apparatus includes a plurality of insertion assemblies, each having a different tool thereon. These may include a cutter, a stopper for sealing the pipe, and a termination plug for sealing the fitting after an opening which has been cut in the pipe through the fitting by means of a cutter has served its purpose.
The means for attaching the barrel to the pipe is in line with the barrel so that, as tools are inserted into the pipe through the barrel exert pressure against the pipe, the pipe is not bent, because the point where the tool bears against the pipe is directly supported by the attaching means.
The attaching means includes a pair of interfacing clamping members, at least one of which includes an arcuate portion that is pressed against the pipe as the attaching means is tightened, forcing the pipe into a round configuration from the slightly-elliptical configuration which pipe normally tends to assume.
It is a further significant advantage of the apparatus just described that the fixture is centered on the branching-saddle pipe stub and in that the attachment means is effective to so mount the fixture on the pipe that the fixture is exactly square on the pipe, i.e., so that the centerline of the fixture is exactly at 90.degree. to the centerline of the pipe. Because of the above relationships, when the fixture is attached to the pipe, the extension stub, which extends into the fixture, is oriented by the fixture so that the stub's centerline is at right angles to the centerline of the pipe, causing tools which enter through the pipe stub with a close fit to be aligned by the pipe stub so that the tools enter the pipe with their centerlines exactly at 90.degree. to the centerline of the pipe.
The first insertion assembly serves to carry a cutting tool through the fixture to bore a hole through the wall of the pipe with the tool. It includes a shaft, a shell cutter mounted on and extending axially from one of the ends of the shaft, and a threaded lead hub non-rotatably mounted on the shaft coaxially therewith. The lead hub is spaced apart from the cutter and is restricted against axial movement along the shaft. A threaded sealing plug is slidably mounted coaxially on the shaft between the cutter and the lead hub and is adapted to receive the lead hub when the shaft is slid through the plug so that the lead hub may be screwed into the sealing plug by rotating the shaft, whereby the shaft and the cutter thereon are axially advanced relative to the sealing plug. Advantageously, the sealing plug has a set of external threads and is adapted to be screwed into the internally-threaded inlet of the barrel of the fixture. With the sealing plug so anchored in the fixture's threaded inlet, and with the threaded engagement of the lead hub in the sealing plug, the cutter may be advanced toward the pipe and rotated so as to effect its cutting action by turning the shaft, thereby screwing the lead hub into the sealing plug.
In further implementing this aspect of the apparatus, there is provided a shell cutter adapted for use with the last-recited insertion assembly which serves not only to cut a hole in the side of the pipe by removing a segment called a "coupon" therefrom, but which is also effective in capturing the coupon so that it does not fall inside the pipe and in capturing shavings which are a by-product of the cutting process inside the cutter. The cutter comprises a cylindrical wall terminating in a cutting end and a plurality of circumferentially-distributed slots in the wall extending from the cutting end at an angle to the axis of the cylindrical wall and terminating in an arcuate cutout. Each section of the cylindrical wall extending between adjacent pairs of slots comprises a tooth of the cutter and has an end face which is inclined relative to a plane which is orthogonal to the axis of the cylindrical wall. An annular cutting ridge extends across the inside surfaces of the teeth so that, as the teeth bite progressively deeper into the pipe during the cutting process, the cutting ridge bites into the sides of the coupon being cut from the pipe, so engaging it that, when the cutter is withdrawn, it continues to grab the coupon and retains it within itself. Furthermore, the combined action of rotating the cutter and the circumferentially-distributed slots results in shavings passing up, through the slots and the arcuate cutouts, into the space in the cutter, above the coupon, so that both shavings and coupon are removed when the cutter is withdrawn.
Another assembly provided with the described apparatus is an insertion assembly for installing a completion plug in a branching saddle, the assembly comprising a tube having a camming groove at one of its ends, a shaft extending through the tube, and a spring-loaded socket extending partially into the grooved end of the tube and biased against further movement into the tube. Detachably carried on the grooved end of the tube is a plug which is adapted to be inserted by means of the tube into the branching saddle. The plug comprises an elastomeric disk sandwiched between a pair of pressure plates, the disk and plates being mounted on a common bolt and locked together by a nut on the bolt and retained thereon, one of the plates having means engageable with the camming groove to hold the plug in place on the tube when the retaining nut is pressed into the spring-loaded socket. Accordingly, the plug may be lowered into place in the branching saddle by means of the tube, and the elastomeric disk may be expanded grippingly into place in the branching saddle by turning the shaft within the tube, thereby driving the retaining nut along the bolt and driving the plates toward each other. The completion plug is installed immediately after the installation of a bypass stopper into the pipe, in accordance with the present invention.
Finally, there is provided means for inspecting the pipe after each of several of the operations have been performed by the various insertion assemblies. The inspection device comprises a plug having a transparent core, the plug being insertable into the same inlet through which the insertion assemblies are admitted into the fixture. Preferably, the inspection device is in the form of an internally-threaded metal cylinder into which is screwed an externally-threaded plexiglass plug, with the internally-threaded cylinder also containing an electric light whereby the pipe may be illuminated and visually inspected by viewing it through the transparent core of the inspection device and through the bore of the fixture.